Confirmation of the zircon age holds enormous implications for models of early Earth. Trace elements in the oldest zircons from Australia’s Jack Hills range suggest they came from water-rich, granite-like rocks such as granodiorite or tonalite. That means Earth cooled down just 100 million years after the massive collision that formed the Earth-moon system.

“The zircons show us the earliest Earth was more like the Earth we know today,” Valley said. “It wasn’t an inhospitable place.”